John and Joséphine decided to build a museum to house their extensive collections of European fine and decorative art. They chose Barnard Castle as the nearest town to Streatlam Castle, John’s main residence in England. The French architect Jules Pellechet, who had worked for them in France, designed the building, although alterations were made later. The French style architecture is thought to be based on that of the town hall in Le Havre.
A local architect and builder, J.E. Watson of Newcastle and Joseph Kyle, were employed to carry through the construction work. Many of the workers, and some of the suppliers, were local people.
Joséphine’s death in 1874, less than five years after she laid the foundation stone, coupled with John’s financial problems, meant that the Museum was still not complete when John died in 1885. Responsibility for finishing the work fell to the Trustees appointed under the wills of Joséphine and John. The Museum opened to the public in 1892.